The Washington-based Center for Strategic and International Studies, the think tank that obtained and analyzed the images, said it spotted the activity at the Sohae (Tongchang-ri) launch facility in northwestern North Korea.

The Trump-Kim summit ended abruptly Feb. 28 after the two leaders could not agree on how to scale down North Korea's nuclear program. Kim wanted sanctions relief for dismantling parts of its nuclear facilities. Trump wasn't willing to give it.

The satellite images were taken March 2.

"We have to solve the problem," Trump told reporters Wednesday. "It will ultimately get solved."

A man watches a TV screen showing a satellite launching facility in North Korea.

Joel Wit, a former official at the State Department and the founder of 38 North, a North Korea monitoring website, cautioned against reading too much into the report.

"There is no evidence #DPRK (North Korea) rebuilding of facilities is consistent with preparations for an ICBM (intercontinental ballistic missile) test," he wrote on Twitter.

"Aside from the fact that #DPRK has never tested an ICBM from Sohae – it's a space launch vehicle launch site – preparation for any launch would require a wide range of activities not observed in the imagery," he added.

North Korea earlier agreed to close the Sohae site as part of a trust-building exercise with South Korea's President Moon Jae-in. Previous satellite pictures, taken in August, indicated that workers had started dismantling the facility.

Sohae has been used in the past for satellite launches that use intercontinental ballistic missile technology banned under United Nations Security Council resolutions.

It is not a nuclear facility.

CSIS described North Korea's actions at Sohae as "deliberate and purposeful" and a reflection of the nation's "plans to demonstrate resolve in the face of U.S. rejection."